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          <h2 class="post-title" itemprop="name headline">Java方法的定义和使用</h2>
        

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        <p>首先对于方法的最大好处是可以进行重复调用，但是至于说哪些操作要形成方法，这些都要根据项目的实际经验来进行自我总结的。</p>
<h1 id="方法的基本定义"><a href="#方法的基本定义" class="headerlink" title="方法的基本定义"></a>方法的基本定义</h1><p>方法指的是一段可以被重复调用的代码块。</p>
<blockquote>
<p>限制条件：本次所讲解的方法指的是在主类中定义，并且由主方法直接调用的方法形式。</p>
</blockquote>
<p>在java里面如果想要进行方法的定义，我们可以使用以下的语法使用：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="keyword">static</span> 方法返回值 方法名称（[参数类型 变量，.....]）&#123;</span><br><span class="line"></span><br><span class="line">       方法体代码；</span><br><span class="line"></span><br><span class="line">       [<span class="keyword">return</span> [返回值] ；]</span><br><span class="line"></span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>定义方法的时候对于方法的返回值有以下的两类：</p>
<ul>
<li>void：没有返回值；</li>
<li>数据类型（基本类型，引用类型）；</li>
</ul>
<p>范例：定义一个没有返回值，没有参数的方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Fangfa</span></span>&#123;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span> </span>&#123;</span><br><span class="line">		print();</span><br><span class="line">		print();</span><br><span class="line">		print();</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">print</span><span class="params">()</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"*************"</span>);</span><br><span class="line">		System.out.println(<span class="string">"*Hello world*"</span>);</span><br><span class="line">		System.out.println(<span class="string">"*************"</span>);</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p> 范例：定义一个有参数无返回值的方法</p>
 <figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"> <span class="comment">//有参数无返回值的方法</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Fangfa1</span></span>&#123;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span> </span>&#123;</span><br><span class="line">		print(<span class="string">"hello"</span>);</span><br><span class="line">		print(<span class="string">"world"</span>);</span><br><span class="line">		print(<span class="string">"kai"</span>);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">print</span><span class="params">(String str)</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"*************"</span>);</span><br><span class="line">		System.out.println(<span class="string">"*"</span>+str+<span class="string">"*"</span>);</span><br><span class="line">		System.out.println(<span class="string">"*************"</span>);</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>范例：有参数有返回值的方法</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//有参数有返回值的方法</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Fangfa2</span></span>&#123;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span> </span>&#123;</span><br><span class="line">		<span class="keyword">int</span> result = add(<span class="number">10</span>,<span class="number">20</span>);</span><br><span class="line">		System.out.println(result);</span><br><span class="line">		<span class="comment">//既然方法有返回值，那么这些返回值也可以直接输出</span></span><br><span class="line">		System.out.println(add(<span class="number">100</span>,<span class="number">200</span>));</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">add</span><span class="params">(<span class="keyword">int</span> x,<span class="keyword">int</span> y)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> x+y;</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<blockquote>
<p>但是在定义方法的时候有一点要特别注意，如果某一个方法上使用了void定义（无返回值），那么该方法可以直接用return来结束调用。一般而言，这种return往往需要结合if判断来实现。</p>
</blockquote>
<p>范例：</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Fangfa3</span></span>&#123;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span> </span>&#123;</span><br><span class="line">		print(<span class="number">10</span>);</span><br><span class="line">		print(<span class="number">20</span>);</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">print</span><span class="params">(<span class="keyword">int</span> x)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">if</span>(x == <span class="number">20</span>) &#123;</span><br><span class="line">			<span class="keyword">return</span>;</span><br><span class="line">		&#125;</span><br><span class="line">		System.out.println(<span class="string">"x = "</span> + x);</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>对于第一次接触方法的人来讲，先将语法记住了，至于怎么用需要时间来消化。</p>
<h1 id="方法重载（重点）"><a href="#方法重载（重点）" class="headerlink" title="方法重载（重点）"></a>方法重载（重点）</h1><p>方法重载指的是：方法的名称相同，参数的类型或个数不同。</p>
<p>范例：实现方法重载</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//方法重载</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Fangfa4</span></span>&#123;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span> </span>&#123;</span><br><span class="line">		System.out.println(add(<span class="number">10</span>,<span class="number">20</span>));</span><br><span class="line">		System.out.println(add(<span class="number">10</span>,<span class="number">20</span>,<span class="number">30</span>));</span><br><span class="line">		System.out.println(add(<span class="number">1.1</span>,<span class="number">2.2</span>));</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">add</span><span class="params">(<span class="keyword">int</span> x,<span class="keyword">int</span> y)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> x + y;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">add</span><span class="params">(<span class="keyword">int</span> x,<span class="keyword">int</span> y,<span class="keyword">int</span> z)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> x + y + z;</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">double</span> <span class="title">add</span><span class="params">(<span class="keyword">double</span> x,<span class="keyword">double</span> y)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">return</span> x + y;</span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>在进行方法重载的时候，有一个重要的原则：要求方法的返回值类型一定要相同。</p>
<p>范例：观察如下的程序</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Fangfa5</span></span>&#123;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span> </span>&#123;</span><br><span class="line">		System.out.println(<span class="string">"hello"</span>); <span class="comment">//输出字符串</span></span><br><span class="line">		System.out.println(<span class="string">"A"</span>); <span class="comment">//输出字符</span></span><br><span class="line">		System.out.println(<span class="number">1</span>);   <span class="comment">//输出整型</span></span><br><span class="line">		System.out.println(<span class="keyword">true</span>);<span class="comment">//输出布尔</span></span><br><span class="line">		System.out.println(<span class="number">1.1</span>);<span class="comment">//输出浮点型</span></span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>证明，System.out.println(）是一个被重载的方法。</p>
<h1 id="方法递归调用（了解）"><a href="#方法递归调用（了解）" class="headerlink" title="方法递归调用（了解）"></a>方法递归调用（了解）</h1><p>方法的递归调用指的是一个方法自己调用自己的形式。</p>
<p>递归：</p>
<ul>
<li>方法必须有一个递归的结束条件</li>
<li>方法在每次递归处理的时候一定要做出一些变更</li>
</ul>
<p>范例：实现1-100的累加操作</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//方法递归实现1-100的加和</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Fangfa6</span></span>&#123;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span> </span>&#123;</span><br><span class="line">		System.out.println(num(<span class="number">100</span>));</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">int</span> <span class="title">num</span><span class="params">(<span class="keyword">int</span> x)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">if</span>(x == <span class="number">1</span>) &#123;      <span class="comment">//结束条件</span></span><br><span class="line">			<span class="keyword">return</span> <span class="number">1</span>;</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">return</span> x + num(x - <span class="number">1</span>);  <span class="comment">//做出变更</span></span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>【调用】第一次执行sum（）方法，主方法执行。return 100 + sum（100-1）；<br>【递归】第二次执行sum（）方法：return 99 + sum（99-1）；<br>【递归】第二次执行sum（）方法：return 98+ sum（98-1）；<br>…..</p>
<p>范例：60！计算</p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//方法递归实现60！</span></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Fangfa7</span></span>&#123;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String args[])</span> </span>&#123;</span><br><span class="line">		System.out.println(nul(<span class="number">60</span>));</span><br><span class="line">	&#125;</span><br><span class="line">	<span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">double</span> <span class="title">nul</span><span class="params">(<span class="keyword">int</span> x)</span> </span>&#123;</span><br><span class="line">		<span class="keyword">if</span>(x == <span class="number">1</span>) &#123;      <span class="comment">//结束条件</span></span><br><span class="line">			<span class="keyword">return</span> <span class="number">1</span>;</span><br><span class="line">		&#125;</span><br><span class="line">		<span class="keyword">return</span> x * nul(x - <span class="number">1</span>);  <span class="comment">//做出变更</span></span><br><span class="line">	&#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>通过代码可以发现使用while循环的操作其实大部分都可以更换为递归，之所以使用递归主要是一个方法可以执行的操作很多，而且结构要好。</p>
<blockquote>
<p>关于java基础学习阶段的代码详见<a href="https://github.com/7666/java_base" target="_blank" rel="noopener">Github</a></p>
</blockquote>

      
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